In Mad Max 2, it was originally going to be revealed near the end of the film that Lord Humungus was in fact Max's old Main Force Patrol partner Jim Goose, who was horribly burned (but not confirmed to be dead) in the first movie. While this didn't make it into the film, some elements of the final product might be leftover hints:
Humungus' scoped pistol is a very similar weapon to the standard sidearm used by the MFP (albeit a different model)note for the record, MFP's issue weapon is a Smith and Wesson Model 28, the utility version of the Model 27, the first .357 Magnum revolver. Humungus uses a .44 Magnum Model 29., and other members of his pack use modified police patrol vehicles.
He appears to have terrible burn scars underneath his mask, as evidenced by the back of his head, though the rest of his body is completely unblemished.
His speeches about losing the people you care about and "ending the suffering" seem to hint at a more conflicted and tragic personality.
Mel Gibson got the part in the first movie because the night before he'd been in a bar fight and only showed up at the casting because he was supporting his friend who was auditioning. He was so beat up that when he came back a few weeks later, they almost didn't recognize him.